====== Switches ======

===== Syntax =====

== Voltage controlled switch ==

Device:

  Sxxxxxxx (n+ n- nc+ nc-) modelname ic

Model (required):

  .model modelname SW args


== Current controlled switch ==

Device:
  Wxxxxxxx (n+ n- ce) modelname ic

Model (required):

  .model modelname CSW args

===== Purpose =====

Voltage or current controlled switch.

===== Comments ======

//N+// and //n-// are the positive and negative element nodes, respectively.

For voltage controlled switch, //Nc+// and //nc-// are the controlling nodes.

For current controlled switch, //ce// is the name of a controlling element.

//Modelname// is the model name.

A switch is a resistor between //n+// and //n-//.  The value of
the resistor is determined by the state of the switch.

^control                 ^resistance  ^
|vc > von\\  ic > ion    |Ron         |
|vc < voff\\  ic < ioff  |Roff        |
|otherwise               |no change   |

You may specify ''ON'' or ''OFF'' to indicate the initial state
of the switch when the controlling voltage is in the hysteresis
region.

The parameters //ron// and //roff// must have finite positive values.
===== Model Parameters =====

^Voltage controlled switch  ^^
|vt    |Threshold voltage.  (Default = 0.)         |
|vh    |Hysteresis voltage.  (Default = 0.)        |
|von   |On control voltage.  (Default = vt + vh)   |
|voff  |Off control voltage.  (Default = vt - vh)  |
|ron   |On resistance.  (Default = 1.)             |
|roff  |Off resistance.  (Default = 1e12)          |

^Current controlled switch  ^^
|it    |Threshold current.  (Default = 0.)         |
|ih    |Hysteresis current.  (Default = 0.)        |
|ion   |On control current.  (Default = it + ih)   |
|ioff  |Off control current.  (Default = it - ih)  |
|ron   |On resistance.  (Default = 1.)             |
|roff  |Off resistance.  (Default = 1e12)          |

===== Time step control =====

A change of state is considered to be an analog event.  An input
crossing a threshold is a "cross event".  Cross events will generate
extra time steps so the switch timing is accurate.

A switch can be used anywhere in a circuit to improve timing accuracy
by sensing cross events.

Switches also influence time step control as resistors, which control
smoothness by curve fitting.

===== Convergence =====

Switches are linear devices that do not iterate unless there is a state change.